The present invention generally relates to electronic circuits having in-phase and quadrature channels, and more particularly, to a gain controller for such circuits.
Receiver circuits and transmitter circuits (collectively xe2x80x9cradio circuitsxe2x80x9d) of the direct conversion type are often used for radio frequency (RF) filtering in communication devices such as mobile phones, television receivers or the like.
Such a radio circuit uses signal pairs having an in-phase signal (I) and a quadrature signal (Q). Both signals I and Q have a substantially equal carrier frequency. The Q signal is 90xc2x0 phase shifted to the I signal. In other words, both signals are in quadrature to each other.
The radio circuit has a first channel for the I signal and second channel for Q signal. Each channel independently forwards and processes its signal, for example by digital-to-analog converting and low-pass filtering. Other signal processing is also possible, for example, analog-to-digital converting. Exact processing of the I and Q signals requires, among other things, that both signals have the same amplitude.
However, differences in the gains (amplitude transfer function) of the channels commonly occur as a result of changes in temperature, frequency, manufacturing variations of the electrical components and other parameters. Small gain differences, (xe2x80x9cmismatchxe2x80x9d) can result in distortions that lead to unwanted discrete tones in further circuitry coupled to the radio circuit. Useful references can be found in U.S. Pat. Nos. 5,604,929; 5,249,203; 5,230,099; 5,179,730; 5,095,536; 5;095;533, all to Looper; as well as in U.S. Pat. No. 4,926,443 to Reich; U.S. Pat. No. 4,633,315 to Kasperkovitz; U.S. Pat. No. 5,930,286 to Walley; and U.S. Pat. No. 4,799,212 to Mehrgardt.
The present invention seeks to provide an improved gain controller which mitigates or avoids disadvantages and limitations of the prior art.